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Can a class create a class within itself?
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Topic: Can a class create a class within itself? (Read 831 times)
petejones
New Member
Posts: 13
Can a class create a class within itself?
«
on:
May 19, 2022, 10:37:40 pm »
Can a class create a class within itself? Here is the code:
type
TParameter = class(TObject)
private
ParamValue: Variant;
ParamType: TParameterType;
end;
type
TParameters = class
public
Items: specialize TFPGObjectList<TParameter>;
constructor Create();
procedure Add(ParameterValue: Variant; ParameterType: TParameterType);
end;
I want the TParameters class to create the Items list when an instance of the TParameters class is created. Is this possible?
Thanks
Pete
Logged
Thausand
Sr. Member
Posts: 292
Re: Can a class create a class within itself?
«
Reply #1 on:
May 19, 2022, 10:54:37 pm »
specialize:
Code: Pascal
[Select]
[+]
[-]
type
TParameterList
=
specialize TFPGObjectList<TParameter>
;
Create:
Code: Pascal
[Select]
[+]
[-]
constructor
TParameters
.
Create
;
begin
inherited
;
Items
:
=
TParameterList
.
Create
;
end
;
Free:
Code: Pascal
[Select]
[+]
[-]
destructor
TParameters
.
Destroy
;
begin
Items
.
Free
;
end
;
How to add:
Code: Pascal
[Select]
[+]
[-]
procedure
TParameters
.
Add
(
ParameterValue
:
Variant
;
ParameterType
:
TParameterType
)
;
var
Parameter
:
TParameter
;
begin
Parameter
:
=
TParameter
.
Create
;
Parameter
.
ParamValue
:
=
ParameterValue
;
Parameter
.
ParamType
:
=
ParameterType
;
Items
.
Add
(
Parameter
)
;
end
;
«
Last Edit: May 19, 2022, 11:05:33 pm by Thausand
»
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #2 on:
May 19, 2022, 11:33:32 pm »
Thanks
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #3 on:
May 20, 2022, 02:21:17 pm »
I'm getting an error to do with the constructor - when I put a breakpoint on Items:=TParameterList.Create and step over that line, Items isn't set to anything and I get a SIGSEGV error when I attempt to add to Items.
Any ideas?
«
Last Edit: May 20, 2022, 02:34:39 pm by petejones
»
Logged
howardpc
Hero Member
Posts: 4144
Re: Can a class create a class within itself?
«
Reply #4 on:
May 20, 2022, 03:52:42 pm »
My best idea is to get you to share a compilable project that gives the error.
Then others can pinpoint its cause quickly without have to guess or make assumptions about what the rest of your code might contain.
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #5 on:
May 20, 2022, 04:54:39 pm »
Good idea, I've attached a zip of the test project.
Cheers
Pete
Logged
Thausand
Sr. Member
Posts: 292
Re: Can a class create a class within itself?
«
Reply #6 on:
May 20, 2022, 05:11:07 pm »
not good:
Code: Pascal
[Select]
[+]
[-]
Parameters
.
Create
;
Parameters
.
Add
(
'Test'
,
TParameterType
.
TText
)
;
Parameters
.
Free
;
better:
Code: Pascal
[Select]
[+]
[-]
Parameters
:
=
TParameters
.
Create
;
Parameters
.
Add
(
'Test'
,
TParameterType
.
TText
)
;
Parameters
.
Free
;
Is not point you ask how to create class ? Then you forget to do
Logged
petejones
New Member
Posts: 13
Re: Can a class create a class within itself?
«
Reply #7 on:
May 20, 2022, 05:21:42 pm »
Ah yes, thanks!
Logged
howardpc
Hero Member
Posts: 4144
Re: Can a class create a class within itself?
«
Reply #8 on:
May 20, 2022, 05:35:58 pm »
While you can use generics, as you do, I think generics + variants is somewhat overkill.
I would simply use a TFPObjectList from contnrs unit.
Logged
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Can a class create a class within itself?
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